What is radon-222? Is it a potential outdoor or indoor pollutant?
It would be a potential pollutant only indoors.
Radon-222 is a naturally occurring isotope of radon. It is potentially harmful because it is radioactive. It should not be considered as a “pollutant” outdoors because it is present only in very dilute, non-harmful concentrations. Because it can accumulate in enclosed spaces, it may become an indoor pollutant primarily in basements where it was present in either the surrounding soil or in the brick materials used to construct a foundation.